Mark dead databases as "dead" and don't dump, probe, or list them

Summary:
When we delete a database, we still need to create it in the patch sequence so that installs can upgrade correctly. However, we shouldn't try to dump, probe, or list it. Mark deleted databases (of which there is only one) as "dead" and don't dump them.

A specific problem this fixes is `bin/storage dump` failing when trying to dump `phabricator_timeline`, which no longer exists.

Test Plan: Ran `bin/storage dump`, `list`, `probe`.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D6496